Method of preferential silicon nitride etching using sulfur hexafluoride

ABSTRACT

Embodiments of the invention describe substrate processing methods using non-polymerizing chemistry to preferentially etch silicon nitride relative to other materials found in semiconductor manufacturing. According to one embodiment, a processing method includes providing in a plasma processing chamber a substrate containing a first material containing silicon nitride and a second material that is different from the first material, forming a plasma-excited process gas containing SF 6 , and exposing the substrate to the plasma-excited process gas to preferentially etch the first material relative to the second material. In one example, the process gas can contain or consist of SF 6  and Ar. In another example, the second material is selected from the group consisting of Si and SiO 2 .

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and claims priority to U.S. ProvisionalPatent Application Ser. No. 62/447,769 filed on Jan. 18, 2017, theentire contents of which are herein incorporated by reference.

FIELD OF INVENTION

The present invention relates to the field of semiconductormanufacturing and semiconductor devices, and more particularly, to amethod of preferential silicon nitride etching relative to othermaterials used in semiconductor manufacturing.

BACKGROUND OF THE INVENTION

Next generation semiconductor technology development poses a hugechallenge as dry etch removal of silicon nitride (SiN) selective tosilicon oxide (SiO₂) and other materials is needed. Current fluorocarbonchemistry used for SiN etch becomes extremely difficult to control atnarrow mask openings and high aspect ratio due to possibility ofclogging of recessed features and the process margin diminishes witheach subsequent technology node. Hence the need for a new chemistryapproaches that are free from fluorocarbon deposition and bypassesadditional challenges of existing processes.

SUMMARY OF THE INVENTION

Embodiments of the invention describe substrate processing methods usingnon-polymerizing chemistry to preferentially etch silicon nitriderelative to other materials used in semiconductor manufacturing.

According to one embodiment, the method includes providing a substratecontaining a first material containing silicon nitride and a secondmaterial that is different from the first material, forming aplasma-excited process gas containing sulfur hexafluoride (SF₆), andexposing the substrate to the plasma-excited process gas topreferentially etch the first material relative to the second material.In one example, the second material may be selected from the groupconsisting of Si and SiO₂. In one example, the process gas may consistof SF₆ and Ar.

According to one embodiment, the method includes providing in a plasmaprocessing chamber a substrate containing a first material containingSiN and a second material selected from the group consisting of Si andSiO₂, forming a plasma-excited process gas containing SF₆ and Ar, andexposing the substrate to the plasma-excited process gas topreferentially etch the first material relative to the second material.

According to one embodiment, the method includes providing in a plasmaprocessing chamber a substrate containing a first material containingSiN and a second material containing SiO₂, forming a plasma-excitedprocess gas containing SF₆ and Ar, and exposing the substrate to theplasma-excited process gas to preferentially etch the first materialrelative to the second material with a SiN/SiO₂ etch selectivity greaterthan 30, where the exposing includes exposing the substrate to ions withkinetic energy that is below a sputtering threshold of the first andsecond materials.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIGS. 1A-1C schematically show through cross-sectional views a method ofprocessing a substrate according to an embodiment of the invention;

FIGS. 2A and 2B schematically show through cross-sectional views amethod of processing a substrate according to an embodiment of theinvention;

FIGS. 3A and 3B schematically show through cross-sectional views amethod of processing a substrate according to an embodiment of theinvention;

FIGS. 4A and 4B schematically show through cross-sectional views amethod of processing a substrate according to an embodiment of theinvention;

FIG. 5 schematically shows an atomic layer deposition (ALD) systemaccording to an embodiment of the invention;

FIG. 6 schematically shows a capacitively coupled plasma (CCP) systemaccording to an embodiment of the invention; and

FIG. 7 shows SiN etch amount, SiO₂ etch amount, and SiN/SiO₂ etchselectivity as a function of plasma process chamber gas pressureaccording to an embodiment of the invention.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

Embodiments of the invention describe substrate processing methods usingnon-polymerizing chemistry to preferentially etch silicon nitride withhigh etch selectivity relative to other materials. In one example,SiN/SiO₂ etch selectivity greater than 30 can be achieved.

FIGS. 1A-1C schematically show through cross-sectional views a method ofprocessing a substrate according to an embodiment of the invention. FIG.1A shows a substrate 100, raised features 102 on the substrate 100, anda SiN spacer layer 104 conformally deposited on the exposed surfaces ofthe raised features 102 and the substrate 100. In this embodiment, theSiN spacer layer 104 is referred to as a first material, and the raisedfeatures 102 are referred to as a second material. The exposed surfacesof the raised features 102 include vertical portions 105 and horizontalportions 103. The substrate 100 and the raised features 102 can, forexample, contain or consist of Si or SiO₂. In one example, the substrate100 consists of Si and the raised features 102 consist of SiO₂. In someexamples of microelectronic devices, the raised features 102 arereferred to as fins. As used herein, the notation “SiN” includesmaterial layers that contain silicon and nitrogen as the majorconstituents, where the layers can have a range of Si and Ncompositions. Si₃N₄ is the most thermodynamically stable of the siliconnitrides and hence the most commercially important of the siliconnitrides. However, embodiments of the invention may be applied to SiNmaterial layers having a wide range of Si and N compositions. An ALDsystem that may be used for depositing the SiN spacer layer 104 isschematically shown in FIG. 6.

A spacer etch process may be performed on the structure shown in FIG. 1Ato form the structure shown in FIG. 1B. The spacer etch process may usefluorocarbon chemistry (e.g., C₄F₆ or CH₃F) to form SiN sidewall spacers106 on the vertical portions 105 of the raised features 102 byanisotropically removing the SiN spacer layer 104 from the horizontalportions 103 of while leaving the SiN spacer layer 104 on the verticalportions 105. Following the formation of the SiN sidewall spacers 106,an anisotropic etching process may be performed to etch recessedfeatures (not shown) in the exposed substrate 100 using the raisedfeatures 102 and the SiN sidewall spacers 106 as a mask.

According to one embodiment, the SiN sidewall spacers 106 are removedfrom the vertical portions 105 of the raised features 102 in a dry etchprocess using a non-polymerizing process gas. The inventors havediscovered that the non-polymerizing process gas provides excellentpreferential dry etching removal of SiN relative to SiO₂ and othermaterials. This is in contrast to currently existing fluorocarbonchemistry used for SiN etching which is extremely difficult to controlat narrow feature openings and high aspect ratio features due to polymerdeposition flux from the fluorocarbon chemistry. The resulting structureis shown in FIG. 1C. The removal of the SiN sidewall spacers 106 may beperformed by plasma-exciting a non-polymerizing process gas containingSF₆ and optionally Ar, and exposing the substrate 100 to theplasma-excited process gas. In some examples, the non-polymerizingprocess gas contains or consists of SF₆ and Ar.

The non-polymerizing process gas may be plasma-excited using a varietyof different plasma sources. According to one embodiment, the plasmasource can include a capacitively coupled plasma (CCP) source thatcontains an upper plate electrode, and a lower plate electrodesupporting the substrate. Radio frequency (RF) power may be provided tothe upper plate electrode, the lower plate electrode, or both, using RFgenerators and impedance networks. A typical frequency for theapplication of RF power to the upper plate electrode ranges from 10 MHzto 200 MHz and may be 60 MHz. In some examples, the upper plateelectrode may be grounded or not powered. Additionally, a typicalfrequency for the application of RF power to the lower plate electroderanges from 0.1 MHz to 100 MHz and may be 13.56 MHz. A CCP system thatmay be used to perform the spacer etch process is schematically shown inFIG. 6. According to another embodiment, a remote plasma source capableof producing high radical to ion flux ratios may be used.

FIGS. 2A and 2B schematically show through cross-sectional views amethod of processing a substrate according to an embodiment of theinvention. FIG. 2A shows a substrate 200, SiN raised features 202 on thesubstrate 200, and sidewall spacers 206 formed on the vertical portions205 of the SiN raised features 202. In this embodiment, the SiN raisedfeatures 202 are referred to as a first material, and the sidewallspacers 206 are referred to as a second material. The horizontalportions 203 of the SiN raised features 202 are exposed by a prior etchprocess. The substrate 200 and the sidewall spacers 206 may, forexample, contain or consist of Si or SiO₂. In one example, the substrate200 consists of Si and the sidewall spacers 206 consist of SiO₂. The SiNraised features 202 are sacrificial features and are often referred toas mandrels, and a subsequent removal of the SiN raised features 202 isoften referred to as a mandrel pull. The structure shown in FIG. 2A maybe formed by creating SiN raised features 202 using conventionaldeposition, lithography, and etch processes. Thereafter, the sidewallspacers 206 may be formed by depositing a conformal layer (not shown) onthe exposed surfaces of the SiN raised features 202 and thereafteranisotropically removing the conformal layer from the horizontalportions 203 using an anisotropic etch process while leaving the layeron the vertical portions 205.

According to one embodiment, the SiN raised features 202 are removedfrom the substrate 200 in a dry etch process. The resulting structurewith free-standing SiN sidewall spacers 206 on the substrate 200 areshown in FIG. 2B. According to an embodiment of the invention, theremoval of the SiN raised features 202 from the substrate 200 includesplasma-exciting a non-polymerizing process gas containing SF₆ andoptionally Ar, and exposing the substrate 200 to the plasma-excitedprocess gas. In some examples, the non-polymerizing process gas containsor consists of SF₆ and Ar.

FIGS. 3A and 3B schematically show through cross-sectional views amethod of processing a substrate according to an embodiment of theinvention. FIG. 3A shows a substrate 300, raised features 302 on thesubstrate 300, and a SiN spacer layer 304 conformally formed on theexposed surfaces of the raised features 302 and the substrate 300. Inthis embodiment, the SiN spacer layer 304 is referred to as a firstmaterial, and the raised features 302 are referred to as a secondmaterial. The exposed surfaces of the raised features 302 includevertical portions 305 and horizontal portions 303. The substrate 300 andthe raised features 302 can, for example, contain or consist of Si orSiO₂. In one example, the substrate 300 consists of Si and the raisedfeatures 302 consist of SiO₂. In some examples of microelectronicdevices, the raised features 302 are referred to as fins.

According to an embodiment of the invention, structure in FIG. 3A isexposed to a plasma-excited non-polymerizing process gas containing SF₆and optionally Ar. The resulting structure is shown in FIG. 3B where theSiN spacer layer 304 from FIG. 3A has been thinned in the isotropic etchprocess. In some examples, the non-polymerizing process gas contains orconsists of SF₆ and Ar.

FIGS. 4A and 4B schematically show through cross-sectional views amethod of processing a substrate according to an embodiment of theinvention. FIG. 4A shows a substrate 410, and SiN raised features 412 onthe substrate 410. In this embodiment, the SiN raised features 402 arereferred to as a first material, and the substrate 410 is referred to asa second material. The SiN raised features 412 have a thickness 413 anda height 415 on the substrate 410. The substrate 410 can, for example,contain or consist of Si or SiO₂.

According to one embodiment, the SiN raised features 412 are trimmed ina dry etch process by plasma-exciting a non-polymerizing process gascontaining SF₆ and optionally Ar, and exposing the substrate 410 to theplasma-excited process gas. The exposure forms trimmed SiN raisedfeatures 414 having a thickness 417 and a height 419, where thethickness 417 is less than the thickness 413, and the height 419 is lessthan the height 415. In one example, the non-polymerizing process gascontains or consists of SF₆ and Ar. The exposure to the plasma-excitedprocess gas may be performed under isotropic processing conditions, forexample by utilizing a remote plasma capable of producing high radicalto ion flux ratios.

Referring back to FIG. 1A, a technique of conformally depositing the SiNspacer layer 104 may include a monolayer deposition (“MLD”) method. TheMLD method may include, for example, an ALD method, which is based onthe principle of the formation of a saturated monolayer of reactiveprecursor molecules by chemisorption. A typical MLD process for formingan AB film, for example, consists of injecting a first precursor orreactant A (“R_(A)”) for a period of time in which a saturated monolayerof A is formed on the substrate. Then, R_(A) is purged from the chamberusing an inert gas, G_(i). A second precursor or reactant B (“R_(B)”) isthen injected into the chamber, also for a period of time, to combine Bwith A and form the layer AB on the substrate. R_(B) is then purged fromthe chamber. This process of introducing precursors or reactants,purging the reactor, introducing another or the same precursors orreactants, and purging the reactor may be repeated a number of times toachieve an AB film of a desired thickness. The thickness of an AB filmdeposited in each ALD cycle may range from about 0.5 angstrom to about2.5 angstrom.

In some embodiments, when forming an AB film, the MLD process mayinclude injecting a precursor containing ABC, which is adsorbed on thesubstrate during the first step, and then removing C during the secondstep.

In accordance with one embodiment of the invention, the SiN spacer layer104 may be deposited by an ALD deposition process in an ALD system, oneexample of which is shown as ALD system 44 in FIG. 5, which includes aprocess chamber 46 having a substrate holder 48 configured to supportthe substrate 14 thereon. The process chamber 46 further contains anupper assembly 50 (for example, a shower head) coupled to a firstprocess material supply system 52 (which may provide asilicon-containing gas), a second process material supply system 54(which may provide a nitrogen-containing gas), a purge gas supply system56, and one or more auxiliary gas supply systems 58 (which may provide adilution gas, or other gases as necessary for depositing the desiredspacer layer material), and a substrate temperature control system 60.

A controller 62 may be coupled to one or more additionalcontrollers/computers (not shown), which may obtain setup and/orconfiguration information from the additional controllers/computers. Thecontroller 62 may be used to configure any number of the processingelements 52, 54, 56, 58, 60, and may collect, provide, process, store,and/or display data from the same. The controller 62 may comprise anumber of applications for controlling one or more of the processingelements 52, 54, 56, 58, 60, and may, if desired, include a graphicaluser interface (“GUI,” not shown) that may provide an easy to useinterface for a user to monitor and/or control one or more of theprocessing elements 52, 54, 56, 58, 60.

The process chamber 46 is further coupled to a pressure control system64, including a vacuum pumping system 66 and a valve 68, through a duct70, wherein the pressure control system 64 is configured to controllablyevacuate the process chamber 10 to a pressure suitable for forming theSiN spacer layer 104 and suitable for use of the first and secondprocess materials. The vacuum pumping system 66 may include aturbo-molecular vacuum pump (“TMP”) or a cryogenic pump that is capableof a pumping speed up to about 5000 liters per second (and greater) andthe valve 68 may include a gate valve for throttling the chamberpressure. Moreover, a device (not shown) for monitoring the chamberprocess may be coupled to the processing chamber 46. The pressurecontrol system 64 may, for example, be configured to control the processchamber pressure between about 0.1 Torr and about 100 Torr during an ALDprocess.

The first and second material supply systems 52, 54, the purge gassupply system 56, and each of the one or more auxiliary gas supplysystems 58 may include one or more pressure control devices, one or moreflow control devices, one or more filters, one or more valves, and/orone or more flow sensors. The flow control devices may include pneumaticdriven valves, electro-mechanical (solenoidal) valves, and/or high-ratepulsed gas injection valves. According to embodiments of the invention,gases may be sequentially and alternately pulsed into the processingchamber 46, where the length of each gas pulse may, for example, bebetween about 0.1 second and about 100 seconds. Alternately, the lengthof each gas pulse may be between about 1 second and about 10 seconds.Exemplary gas pulse lengths for silicon- and nitrogen-containing gasesmay be between about 0.3 second and about 3 seconds, for example, about1 second. Exemplary purge gas pulses may be between about 1 second andabout 20 seconds, for example, about 3 seconds. Still referring to FIG.5, the controller 62 may comprise a microprocessor, memory, and adigital I/O port capable of generating control voltages sufficient tocommunicate and activate inputs to the ALD system 44, as well as monitoroutputs from the ALD system 44. Moreover, the controller 62 may becoupled to and may exchange information with the process chamber 46, thesubstrate holder 48, the upper assembly 50, the processing elements 52,54, 56, 58, the substrate temperature controller 60, and the pressurecontrol system 64. For example, a program stored in a memory of thecontroller 62 may be utilized to activate the inputs to theaforementioned components of the ALD system 44 according to a processrecipe in order to perform a deposition process.

The controller 62 may be implemented as a general purpose computersystem that performs a portion or all of the microprocessor-basedprocessing steps of the present invention in response to a processorexecuting one or more sequences of one or more instructions contained ina memory. Such instructions may be read into the controller memory fromanother computer readable medium, such as a hard disk or a removablemedia drive. One or more processors in a multi-processing arrangementmay also be employed as the controller microprocessor to execute thesequences of instructions contained in main memory. In alternativeembodiments, hard-wired circuitry may be used in place of or incombination with software instructions. Thus, embodiments are notlimited to any specific combination of hardware circuitry and software.

The controller 62 includes at least one computer readable medium ormemory, such as the controller memory, for holding instructionsprogrammed according to the teachings of the invention and forcontaining data structures, tables, records, or other data that may benecessary to implement the present invention. Examples of computerreadable media are hard disks, floppy disks, tape, magneto-opticaldisks, PROMs (EPROM, EEPROM, flash EPROM), DRAM, SRAM, SDRAM, or anyother magnetic medium, compact discs (e.g., CD-ROM), or any otheroptical medium, punch cards, paper tape, or other physical medium withpatterns of holes, a carrier wave (described below), or any other mediumfrom which a computer can read.

Stored on any one or on a combination of computer readable media,resides software for controlling the controller 62, for driving a deviceor devices for implementing the present invention, and/or for enablingthe controller 62 to interact with a human user. Such software mayinclude, but is not limited to, device drivers, operating systems,development tools, and applications software. Such computer readablemedia further includes the computer program product of the presentinvention for performing all or a portion (if processing is distributed)of the processing performed in implementing the present invention.

The computer code devices may be any interpretable or executable codemechanism, including but not limited to scripts, interpretable programs,dynamic link libraries (“DLLs”), Java classes, and complete executableprograms. Moreover, parts of the processing of the present invention maybe distributed for better performance, reliability, and/or cost.

The term “computer readable medium” as used herein refers to any mediumthat participates in providing instructions to the processor of thecontroller 62 for execution. Thus, computer readable medium may takemany forms, including but not limited to, non-volatile media, volatilemedia, and transmission media. Non-volatile media includes, for example,optical, magnetic disks, and magneto-optical disks, such as the harddisk or the removable media drive. Volatile media includes dynamicmemory, such as the main memory. Moreover, various forms of computerreadable media may be involved in carrying out one or more sequences ofone or more instructions to the processor of the controller 62 forexecution. For example, the instructions may initially be carried on amagnetic disk of a remote computer. The remote computer can load theinstructions for implementing all or a portion of the present inventionremotely into a dynamic memory and send the instructions over a networkto the controller 62.

The controller 62 may be locally located relative to the ALD system 44,or it may be remotely located relative to the ALD system 44. Forexample, the controller 62 may exchange data with the ALD system 44using at least one of a direct connection, an intranet, the Internet anda wireless connection. The controller 62 may be coupled to an intranetat, for example, a customer site (i.e., a device maker, etc.), or it maybe coupled to an intranet at, for example, a vendor site (i.e., anequipment manufacturer). Additionally, for example, the controller 62may be coupled to the Internet. Furthermore, another computer (i.e.,controller, server, etc.) may access, for example, the controller 62 toexchange data via at least one of a direct connection, an intranet, andthe Internet. As also would be appreciated by those skilled in the art,the controller 62 may exchange data with the deposition system 44 via awireless connection.

Deposition of the SiN spacer layer 104 may proceed by sequential andalternating pulse sequences to deposit the different components (here,for example, silicon and nitrogen) of the SiN spacer layer 104 material.Since ALD processes typically deposit less than a monolayer of thecomponent per gas pulse, it is possible to form a homogenous materialusing separate deposition sequences of the different components of thefilm. Each gas pulse may include a respective purge or evacuation stepto remove unreacted gas or byproducts from the process chamber 46.According to other embodiments of the present invention, one or more ofthe purge or evacuation steps may be omitted.

Therefore, and as one exemplary embodiment, the substrate 14 with theprocessed raised features 102 is disposed in the process chamber 46 ofthe ALD system 44 and sequentially exposed to a gas pulse containingsilicon and a gas pulse of a nitrogen-containing gas, the latter ofwhich may include NH₃, plasma-exited nitrogen (such as for use in PEALDsystems), or a combination thereof, and optionally an inert gas, such asargon (Ar).

The silicon may react on the surface of the raised feature 102 to form achemisorbed layer that is less than a monolayer thick. The nitrogen fromthe gas pulse of the nitrogen-containing gas may then react with thechemisorbed surface layer. By repeating this sequential gas exposure,i.e., by alternating the two exposures a plurality of times, it ispossible to achieve layer-by-layer growth of about 1 angstrom (10⁻¹⁰meter) per cycle until a desired thickness is achieved.

Exemplary plasma processing device 500 depicted in FIG. 6 including achamber 510, a substrate holder 520 (lower electrode), upon which asubstrate 525 to be processed is affixed, a gas injection system 540,and a vacuum pumping system 550. Chamber 510 is configured to facilitatethe generation of plasma in a processing region 545 adjacent a surfaceof substrate 525, wherein plasma is formed via collisions between heatedelectrons and an ionizable gas. An ionizable gas or mixture of gases isintroduced via the gas injection system 540 and the process pressure isadjusted. For example, a gate valve (not shown) is used to throttle thevacuum pumping system 550. Desirably, plasma is utilized to creatematerials specific to a pre-determined materials process, and to aideither the deposition of material to a substrate 525 or the removal ofmaterial from the exposed surfaces of the substrate 525.

Substrate 525 is transferred into and out of chamber 510 through a slotvalve (not shown) and chamber feed-through (not shown) via roboticsubstrate transfer system where it is received by substrate lift pins(not shown) housed within substrate holder 520 and mechanicallytranslated by devices housed therein. Once the substrate 525 is receivedfrom the substrate transfer system, it is lowered to an upper surface ofthe substrate holder 520.

In an alternate embodiment, the substrate 525 is affixed to thesubstrate holder 520 via an electrostatic clamp (not shown).Furthermore, the substrate holder 520 further includes a cooling systemincluding a re-circulating coolant flow that receives heat from thesubstrate holder 520 and transfers heat to a heat exchanger system (notshown), or when heating, transfers heat from the heat exchanger system.Moreover, gas may be delivered to the back-side of the substrate toimprove the gas-gap thermal conductance between the substrate 525 andthe substrate holder 520. Such a system is utilized when temperaturecontrol of the substrate is required at elevated or reducedtemperatures. For example, temperature control of the substrate may beuseful at temperatures in excess of the steady-state temperatureachieved due to a balance of the heat flux delivered to the substrate525 from the plasma and the heat flux removed from substrate 525 byconduction to the substrate holder 520. In other embodiments, heatingelements, such as resistive heating elements, or thermo-electricheaters/coolers are included.

In a first embodiment, the substrate holder 520 further serves as anelectrode through which radio frequency (RF) power is coupled to plasmain the processing region 545. For example, the substrate holder 520 iselectrically biased at a RF voltage via the transmission of RF powerfrom an RF generator 530 through an impedance match network 532 to thesubstrate holder 520. The RF bias serves to heat electrons and, thereby,form and maintain plasma. In this configuration, the system operates asa reactive ion etch (RIE) reactor, wherein the chamber and upper gasinjection electrode serve as ground surfaces. A typical frequency forthe RF bias ranges from 0.1 MHz to 100 MHz and may be 13.56 MHz. In analternate embodiment, RF power is applied to the substrate holderelectrode at multiple frequencies. Furthermore, the impedance matchnetwork 532 serves to maximize the transfer of RF power to plasma inprocessing chamber 10 by minimizing the reflected power. Match networktopologies (e.g. L-type, π-type, T-type, etc.) and automatic controlmethods are known in the art.

With continuing reference to FIG. 7, a process gas 542 (e.g., containingSF₆ and optionally Ar) is introduced to the processing region 545through the gas injection system 540. Gas injection system 540 caninclude a showerhead, wherein the process gas 542 is supplied from a gasdelivery system (not shown) to the processing region 545 through a gasinjection plenum (not shown), a series of baffle plates (not shown) anda multi-orifice showerhead gas injection plate (not shown).

Vacuum pump system 550 preferably includes a turbo-molecular vacuum pump(TMP) capable of a pumping speed up to 5000 liters per second (andgreater) and a gate valve for throttling the chamber pressure. Inconventional plasma processing devices utilized for dry plasma etch, a1000 to 3000 liter per second TMP is employed. TMPs are useful for lowpressure processing, typically less than 50 mTorr. At higher pressures,the TMP pumping speed falls off dramatically. For high pressureprocessing (i.e. greater than 100 mTorr), a mechanical booster pump anddry roughing pump are used.

A computer 555 includes a microprocessor, a memory, and a digital I/Oport capable of generating control voltages sufficient to communicateand activate inputs to the plasma processing system 500 as well asmonitor outputs from the plasma processing system 500. Moreover, thecomputer 555 is coupled to and exchanges information with the RFgenerator 530, the impedance match network 532, the gas injection system540 and the vacuum pump system 550. A program stored in the memory isutilized to activate the inputs to the aforementioned components of aplasma processing system 500 according to a stored process recipe.

The plasma processing system 500 further includes an upper plateelectrode 570 to which RF power may be coupled from an RF generator 572through an impedance match network 574. A typical frequency for theapplication of RF power to the upper electrode ranges from 10 MHz to 200MHz and is preferably 60 MHz. Additionally, a typical frequency for theapplication of power to the lower electrode ranges from 0.1 MHz to 30MHz. Moreover, the computer 555 is coupled to the RF generator 572 andthe impedance match network 574 in order to control the application ofRF power to the upper electrode 570. According to some embodiments,plasma may be generated in the process chamber 510 by RF-powering thelower electrode 520 while the upper electrode 570 may be grounded or notpowered.

The dry etch of SiN layers using a non-polymerizing process gascontaining SF₆ and optionally Ar, is thought to include the followingetch mechanism that includes generation of F radicals in a plasma,diffusion of F radicals to the Si₃N₄ layer, adsorption of F radicals onthe SiN layer, surface reaction of F with SiN to form SiF₄ etchproducts, and desorption and removal of the SiF₄ etch products from theSiN layer.

FIG. 7 shows SiN etch amount, SiO₂ etch amount, and SiN/SiO₂ etchselectivity as a function of plasma process chamber gas pressureaccording to an embodiment of the invention. The process gas consistedof SF₆ gas and Ar gas that was plasma-excited using a CCP plasma source.The processing conditions included OW applied to an upper plateelectrode, 100 W of RF power at 13.56 MHz applied to a lower plateelectrode supporting the substrate, SF₆ gas flow of 450 sccm and Ar gasflow of 1000 sccm, and plasma exposure time of 300 seconds. The lowerplate electrode (substrate holder) was cooled at 15° C. The gaspressures in the plasma process chamber were 200 mTorr, 300 mTorr, 400mTorr, and 500 mTorr. The experimental results show that SiN/SiO₂ etchselectivity greatly increased at gas pressure above 300 mTorr,increasing from about 5 at 300 mTorr to greater than 38 at 500 mTorr.This unexpectedly high SiN/SiO₂ etch selectivity at gas pressure above300 mTorr corresponds to substantially infinite SiN/SiO₂ etchselectivity for semiconductor manufacturing. Thus, according to oneembodiment, a SiN/SiO₂ etch selectivity greater than 30 may easily beachieved.

It is contemplated that this unexpectedly high SiN/SiO₂ etch selectivityas the gas pressure is increased is at least in part due to decrease inion energy in the plasma, accompanied by an increase in radical flux anda reduction in ion flux exposed to the substrate. Further, the low RFpower (<100 W) applied to the lower plate electrode is below thesputtering threshold of the first and second materials by ions in theplasma-excited process gas. In other words, the ions that are created inthe plasma-excited process gas do not have enough kinetic energy tosputter etch the first and second materials. Therefore, the highSiN/SiO₂ etch selectivity is believed to be entirely due tothermodynamically favored radical etch of SiN relative to SiO₂.

According to one embodiment, a plasma-excited process gas may begenerated using a capacitively coupled plasma (CCP) source containing anupper plate electrode, and a lower plate electrode supporting thesubstrate, where the upper plate electrode is grounded and RF powerapplied to the lower plate electrode creates ions in the plasma havingkinetic energy below the sputtering threshold of the first and secondmaterials. In one example, RF power of about 100 W, or less (e.g., <80W, <60 W, <40 W, etc), may be applied to a lower plate electrode of aCCP system. A frequency of the RF power applied to the lower plateelectrode may be 13.56 MHz. According to some embodiments the SF₆ gasflow can be between about 50 sccm and about 500 sccm, and the Ar gasflow can be between about 0 sccm and about 1000 sccm.

A plurality of embodiments for substrate processing methods usingnon-polymerizing chemistry to preferentially etch silicon nitriderelative to other materials used in semiconductor manufacturing havebeen described. The foregoing description of the embodiments of theinvention has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. This description and theclaims following include terms that are used for descriptive purposesonly and are not to be construed as limiting. Persons skilled in therelevant art can appreciate that many modifications and variations arepossible in light of the above teaching. It is therefore intended thatthe scope of the invention be limited not by this detailed description,but rather by the claims appended hereto.

What is claimed is:
 1. A substrate processing method, comprising:providing in a plasma processing chamber a substrate containing a firstmaterial containing SiN and a second material that is different from thefirst material; forming a plasma-excited process gas containing SF₆,wherein forming the plasma-excited process gas includes generating aplasma using a capacitively coupled plasma source containing an upperplate electrode and a lower plate electrode supporting the substrate,and wherein the upper plate electrode is grounded or not powered andradio frequency (RF) power is applied to the lower plate electrode togenerate the plasma in a processing region between the upper plateelectrode and the lower plate electrode; and exposing the substrate tothe plasma-excited process gas to preferentially etch the first materialrelative to the second material, wherein the exposing includes exposingthe substrate to ions having kinetic energy that is below a sputteringthreshold of the first and second materials, and wherein the kineticenergy of the ions is supplied by the RF power applied to the lowerplate electrode.
 2. The method of claim 1, wherein the second materialis selected from the group consisting of Si and SiO₂.
 3. The method ofclaim 1, wherein the second material includes SiO₂ and a SiN/SiO₂ etchselectivity is greater than
 30. 4. The method of claim 1, wherein,during the exposing, a gas pressure greater than about 300 mTorr ismaintained in the plasma processing chamber.
 5. The method of claim 1,wherein, during the exposing, a gas pressure of about 500 mTorr, orgreater, is maintained in the plasma processing chamber.
 6. The methodof claim 1, wherein the RF power applied to the lower plate electrode isabout 100 W, or less.
 7. The method of claim 1, wherein a frequency ofthe RF power applied to the lower plate electrode is 13.56 MHz.
 8. Themethod of claim 1, wherein the plasma-excited process gas furthercontains Ar.
 9. The method of claim 1, wherein the plasma-excitedprocess gas consists of SF₆ and Ar.
 10. The method of claim 1, whereinthe second material includes raised features on the substrate, the firstmaterial forms sidewall spacers on vertical portions of the raisedfeatures, and the exposing removes the sidewall spacers from the raisedfeatures.
 11. The method of claim 1, wherein the first material includesraised features on the substrate, the second material forms sidewallspacers on vertical portions of the raised features, and the exposingremoves the raised features but not the sidewall spacers.
 12. The methodof claim 1, wherein the second material includes raised features on thesubstrate, the first material forms a conformal film on the raisedfeatures, and the exposing isotropically thins the conformal film.
 13. Asubstrate processing method, comprising: providing in a plasmaprocessing chamber a substrate containing a first material containingSiN and a second material containing SiO₂; forming a plasma-excitedprocess gas containing SF₆ and Ar, wherein forming the plasma-excitedprocess gas includes generating a plasma using a capacitively coupledplasma source containing an upper plate electrode and a lower plateelectrode supporting the substrate, and wherein the upper plateelectrode is grounded or not powered and radio frequency (RF) power isapplied to the lower plate electrode; and exposing the substrate to theplasma-excited process gas to preferentially etch the first materialrelative to the second material with a SiN/SiO₂ etch selectivity greaterthan 30, wherein the exposing includes exposing the substrate to ionswith kinetic energy that is below a sputtering threshold of the firstand second materials, and wherein the kinetic energy of the ions issupplied by the RF power applied to the lower plate electrode.
 14. Themethod of claim 13, wherein, during the exposing, a gas pressure ofabout 500 mTorr, or greater, is maintained in the plasma processingchamber.